Recently, as issues concerned with the environment and energy resources become important, electric vehicles and plug-in hybrid vehicles have been spotlighted as future transportation to solve the issues.
Although power for charging the batteries in the existing hybrid electric vehicles was supplied by a regenerative brake and operating a power generator by the engine, electric vehicles and plug-in hybrid vehicles can be supplied with power for charging the batteries of the electric vehicles from a national grid or a decentralized power supply.
On the other hand, when the electric vehicles and plug-in hybrid vehicles are used for commuting, a pattern of driving the vehicles in the morning and charging the batteries in the evening has an adverse effect on the national grid or the decentralized power supply and increases the highest power consumption of the entire grid at a specific period of time.
This is set to the highest power consumption, but if more power is used, the present power system with a reserve rate of about 10% requires additional equipment for power generation and a large amount of electricity is wasted, thereby reducing energy efficiency.
Therefore, recently, a smart grid system that makes the grid intelligent has been constructed to increase energy efficiency and reduce energy consumption and bilateral horizontal supply systems, such as a microgrid and a decentralized power supply method, have been implemented, coming out of the vertical system that one-sidedly supplies electricity from the central station.
The core of the smart grid system is that consumers and a power company communicate information in real time by combining the grid with an information and communication technology, such as ZigBee or power line communication, which makes it possible to use electricity and automatically operates devices at a period of time with low electric charges.
However, there is a problem in that the existing charging equipment of electric vehicles immediately charge the batteries regardless of the electric charges and this has a considerable adverse effect on the national grid or the decentralized power supply, such that it is difficult to use electricity for charging the batteries of the electric vehicles at low cost.